1. Field of the Invention
This invention relates to pull-tabs for cans of soda and the like, and more particularly concerns a method of making pull-tabs for cans and affixing them to the ends of cans without any unwanted transfer of lubricant from the pull-tabs to the interior of a can end stacked above it, and to substantially reducing the emission into the atmosphere of volatile organic contents (VOCs).
2. Description of the Prior Art
It is conventional in the forming of pull-tabs for cans to take a strip of aluminum and feed it into a progressive die press. There may be seventeen steps in the die press that are taken progressively, with the first die making a little indentation in the strip, the second die making a further indentation, and so on so that by the time the strip gets to the seventeenth step, it has formed a pull-tab that it is then riveted onto the exterior of a can end. This progressive die press operates at a high rate of speed, as anywhere from 550 to 575 strokes per minute. Since the die press stresses the aluminum strip, a lubricant is required to protect the tooling in the die press which is very expensive. These presses run twenty-four hours a day, seven days a week, 365 days a year. When a die press has to be shut down to replace the tooling because it has become dull, the down time becomes expensive. Accordingly, operators of such die presses are always looking for a lubricant that gives them the maximum amount of efficiency and the least amount of down time per year.
A conventional lubricant composition for these presses may be delivered in tank trucks containing 7000 gallons of the lubricant composition, and a delivery may be made every five weeks to just one plant. However, this conventional lubricant composition comprises 6300 gallons of solvent and 700 gallons of lubricant, and so 6300 gallons of the solvent evaporates from the liquid into the atmosphere when the lubricant composition is being used. Since the solvent is a hydrocarbon, this contaminates the atmosphere, and the government is trying to reduce the contamination under the Clean Air Act by limiting the amount of volatile organic contents (VOCs) that go into the atmosphere. The government has put a cap on all plants that emit VOCs so that they cannot release more than a certain amount of VOCs per year. This limitation on VOCs is not limited to conventional lubricants used in die presses, but also includes any other VOC emissions that may come from other substances, such as paint.
Accordingly, many engineers and plant superintendents have been working on the problem and have been looking for a lubricant composition that would lubricate the dies and yet not release unwanted hydrocarbons into the atmosphere. The conventional lubricant formula includes a butyl stearate in a solvent such as alcohol, and the alcohol evaporates and releases the unwanted VOCs into the atmosphere.